As most matters of degree will. I'm just pointing out that it's commensurate to that game's take on what having "completed" a place's open world content looks like. Like you, I'd prefer earlier unlocks (or, remaining requirements being reduced over time), but that design paradigm isn't 'wrong' so much as simply suiting a different context.
Ideally, I'd agree with you, but that's also badly limiting. Imagine, for instance, a zone with many distinct sections with various dangers bordering them. If normally going down south to a few world quests in the Ruins area required that I first take a boat down the river, surviving croc attacks to even get there, or pass through dense jungle rife with panthers, that's still a (enjoyable, imo) component of the open world's dangers that obviously isn't going to be suitably reproducible in each separate activity. Much of the interest of the open world is its connections, its pathing, its optimizing around risks and time taken. All that is gone if you reduce everything therein to isolated activities. That's kind of what separates open world play from our tiny square or circle typical instances in the first place.If you were made to do it without flight once, then that's great. If this is a repeatable quest, then there's no reason to block flying to get there again. Make all the dangers be present at the quest site so you'll still have to fight there when you drop down.
To back up just a bit:
My preferred model, again, is for the open world to be designed to be interesting even under whatever particular tools, ground and flying mounts included (though I'd always go the way of GW2's Griffin over "true", WoW/XIV-like, physics-less free flight), a player may have. It should feel like a playground and optimizing to reduce time or risk should be a real thing, but that requires also it not be simply a single, cheap solution (like limitless flight in a world without aerial threats).
Few MMOs manage that, period, and not just because they letter wreck it with unfettered flight; for many (imo, XIV included) there was little to nothing there to begin with. But, in the few instances where we've seen decent examples of world design, it looks really lucrative, and I'd hate to see that lost over some assumed obligation that everything be made as quick as possible (i.e., that because flight could exist, it should exist, and should exist asap). In that ideal world, I probably wouldn't lock flight behind grinds, but I might well make it a rare mount for which that flight is the only unique power, and I'd try to futureproof the zone around players' eventually acquiring it (as much to give them more fun in the joy of movement they might have via that flight as to curtail what elements they'd otherwise degrade for themselves).